scsi: hpsa: Remove unneeded void pointer cast

It's not necessary to cast the result of kmalloc, since void pointers
are promoted to any other type. This also fixes following coccinelle
warning:

casting value returned by memory allocation function to (BIG_IOCTL_Command_struct *) is useless.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>